Deemed the “most successful public health campaign in modern history,” researchers report that 50 years of tobacco control have saved about 20 years of additional life for eight million Americans.

On Jan. 11, 1964, Dr. Luther Terry, the U.S. surgeon general of the U.S. Public Health Service, released The Surgeon General’s report of 1964, the first such analysis that laid out the effects of tobacco and smoking, and spurred initiatives to lower tobacco use among Americans. Its conclusions were built on more than 7,000 studies on smoking and concluded for the first time that smoking caused lung cancer in men, and likely in women, and that lighting up was the most likely cause of chronic bronchitis.

Now, fifty years later, thanks to Terry’s efforts and those of his successors, a study published in JAMA by researchers from the Cancer Intervention and Surveillance Modeling Network (CSINET) reports that 20% of adult Americans now smoke, compared to 50% in 1964.

In the latest study, the researchers looked at smoking patterns up to 1964 and then estimated what the mortality rates would have been if no tobacco control strategies, such as anti-smoking laws and higher taxes on cigarettes, had been implemented. Then, they compared it to current smoking rates, and estimated that 157 million years of lives have been saved — about 19.6 more years for every smoker who quit.

During the 50 years since the report, the researchers estimated that the life expectancy for adults at age 40 increased 7.8 years for men and 5.4 years for women, and that tobacco control efforts accounted for 2.3 of these additional years for men and 1.6 of them for women.

Still, the researchers says, “Despite the success of tobacco control in reducing premature deaths in the United States, smoking remains a significant public health problem.” Another report, also published in JAMA, found that even though the percentage of the global population that smokes on a daily basis has decreased, the number of smokers has increased due to population growth. The new report showed that overall smoking rates worldwide dropped by 42% among women and 25% among men. Rates in Canada, Mexico, Norway and Iceland have been slashed by more than half.

Population growth, however, means that these rates are not making a significant dent in the absolute numbers of smokers around the world; since 1980, there are 41% more male smokers and 7% more female smokers.

Still, both reports highlight how effective tobacco control can be. “We know from these global trends that rapid progress is possible. If more countries were able to repeat the success we have seen in Norway, Mexico, and the Unites States, we would see much less health loss from smoking,” said Emmanuela Gakidou, a professor of global health and director of education and training at the University of Washington and author of the second study, in a statement.